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William Paley Institute
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Intelligent Design |
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Thinking About the Theory of Design
by Paul Nelson
A Report on the Symposium "Can There be a Scientific Theory of Intelligent
Design?" held at the 48th Annual Meeting of the American Scientific Affiliation,
Seattle Pacific University, Seattle, WA.
August 9, 1993
Introduction: Why Return to a Disreputable Business?
Present theological discussions . . . ignore natural theology, and for
contemporary linguistic philosophers the Argument from Design possesses no
validity whatsoever and is logically and morally indefensible, although it may
serve to heighten religious emotions.
-- Meyrick H. Carre
"Physicotheology," The Encyclopedia of Philosophy
One wonders what religious emotions the argument from design is supposed to
heighten. Presumably they do not themselves make any strong claim to
reasonableness. "All poets," said W.H. Auden, "adore explosions, thunderstorms,
tornadoes, conflagrations, ruins," and "scenes of spectacular carnage."1 And
that is why, perhaps, poets are not generally at the reins of power. "The poetic
imagination," Auden noted ruefully, "is not at all a desirable quality in a
statesman." Analogously, we might observe, any emotion that can be heightened by
a completely invalid and indefensible argument, is hardly one to be encouraged
in the scientific enterprise -- although, to Carre's way of thinking, religion
may have some use for the sentiment.
Is the theory of design (as I shall call it) really as bad as all that?2 Ask
most scientists and philosophers, and the answer will be yes. Design as a
scientific explanation is widely regarded as a dusty museum piece, a device that
ceased to function in the nineteenth century. According to this view, when
design collapsed around 1859 and the wreckage went into a display case, it was
discovered that the theory had been supported all along only by various logical
and theological mistakes. Therefore (it is claimed), if design has anything to
teach us today, the lesson is strictly cautionary. Nowadays all reputable
scientists and philosophers, whatever they may believe away from the lab or
seminar room, are methodological naturalists.
That's the usual story. Looked at closely, however, the usual story has some
remarkable, or fabulous -- meaning genuinely legendary -- passages. It is a
legend, for example, that Charles Darwin solved the problem of the origin of
biological complexity. It is a legend that we have a good or even fair grasp on
the origin of life, or that proper explanations refer only to so-called natural
causes. To be sure, these and other legends of philosophical naturalism have a
certain stature. One does not speak too harshly of them in polite company.
But neither should one accept them uncritically. Indeed, if we view the legends
of philosophical naturalism with justifiable skepticism, the case against design
looks far less formidable. But we can go further. While much work remains to be
done to develop an empirically fruitful theory of design, it appears that none
of the standing objections to design is unanswerable. As those objections are
removed one by one, within the next decade it is quite likely that (in the words
of design theorist Bill Dembski) "a theory of design can be formulated which
will have significant advantages over its Darwin-inspired competitors."
Now before the reader dismisses me for my naive optimism, let me acknowledge
that a profound antipathy to design extends throughout the scientific and
philosophical communities. When all the arguments for the theory have been
weighed, many persons will still conclude that design is a bad idea assembled
from noxious materials, which belongs where it has long resided -- safely behind
glass in the Hall of Great Scientific Failures.
Plainly, I do not think design is a bad idea; when weighed, arguments for design
are, I believe, powerfully compelling. To be weighed, however, arguments for
design must be heard. Thus, in August, the American Scientific Affiliation
(ASA), an organization of Christians in the sciences, convened a symposium on
the theory of design. Those unfamiliar with the ASA might suppose that such a
symposium would be a congress of the already-converted, but that is not the
case. Many of the strongest critics of design as a scientific explanation are
leaders in the ASA, prominent in both its publications and lectures. These
persons argue that they, perhaps better than most, are qualified to find the
theory of design wanting. They are the intellectual offspring of believing
scientists of past generations, who (it is said) found that design, when applied
as a scientific explanation, fell to pieces in one's hands. Thus the ASA was in
many respects a less sympathetic audience for considering design than many
secular audiences might have been.
No poll was taken after the symposium, but in discussions before and after the
talks, the speakers (including myself) discovered great curiosity about the
merits of design as an explanation and cautious encouragement for attempts to
reframe the theory on new foundations. This report brings some of the points
argued to a larger audience. Readers are strongly encouraged to contact the
speakers (c/o Origins Research) with any criticisms or insights. Three of the
speakers (Dembski, Meyer and Nelson) are engaged in a research project on the
theory of design, funded by the Pascal Centre in Ontario, Canada, which will
culminate in a book-length monograph on the subject.
In what follows I review the major points of each talk.
The first speaker, William Dembski, is a University of Chicago-trained
mathematician (Ph.D. 1988), now completing a second Ph.D. in philosophy. Dembski
approaches the theory of design first as a probabilist interested in explicating
the structure of the "ordinary" design inferences that abound in our everyday
life.
These inferences conform under analysis to what Dembski calls "a standard
operating procedure," illustrated by the flow chart in Figure 1. Consider an
example3: John Smith died because his pacemaker malfunctioned. Smith's death due
to pacemaker malfunction is the event, E (the circle at the top of the flow
chart), to be explained. Now suppose that on examining the pacemaker and Smith's
medical history, we discover that the pacemaker battery, although guaranteed to
be fully functional for five years, was certain to run out after seven. Smith
was negligent and forgot to replace the battery. Sure enough, it ran out,
Smith's heart fibrillated, and he died.
In this example we terminate (in explaining E) at the first decision node, HP.
Given the physical principles governing pacemaker batteries and Smith's
negligence, his death from pacemaker malfunction was a high probability, or HP
event, certain or virtually certain to occur. "And if we can explain by
necessity," said Dembski, "chance and design are automatically precluded."
Suppose Smith wasn't negligent, however. Suppose, in fact, that he replaced the
battery just a year ago. Here we pass to the second decision node, IP, or to the
class of intermediate probability events. These events, said Dembski, "are
sufficiently probable as not to be a source of amazement." Smith, it turns out,
fell victim to a chance failure. Pacemaker manufacturers routinely test very
large samples of batteries to ensure that the probability of failure for any
given battery is extremely low. Nevertheless, while unlikely, it is still
possible that before the expected five-year period, some batteries will by
chance fail. Smith came up unlucky in this dreadful lottery. The pacemaker
battery ran out after only one year, his heart fibrillated, and he died. Smith's
death is an IP event. Such chance events occur -- they fill the newspaper -- but
we don't attribute them to design.
Solving a Mystery
Consider another scenario, however. At Smith's autopsy we can find nothing amiss
with his pacemaker -- except for some peculiar damage that we know can be caused
only by exposure to intense microwave radiation. Our suspicions aroused, we
begin an inquest and soon discover the following
1. Jane Doe, Smith's co-worker, rented microwave-transmitting equipment 10 days
before Smith's death.
2. Smith signed a life insurance policy one week before his death, naming Jane
Doe the sole beneficiary.
3. There are scratches on Smith's kitchen floor that correspond exactly to the
dimensions of the microwave equipment.
4. A pamphlet on pacemaker risks, including microwave exposure, is found in Jane
Doe's car.
5. The microwave warning in the pamphlet is underlined.
6. "Get John Smith next week" is written in the margin, next to the underlined
warning, in Jane Doe's handwriting.
7. Witnesses saw Jane Doe leave Smith's house shortly before he was discovered
dead.
The police arrest Jane Doe immediately. She protests her innocence, but the
district attorney jails her anyway and charges her with the pre-meditated murder
of Smith. In the course of a trial the jury convicts her of the crime, and she
is sentenced to life imprisonment.
Why do Jane Doe's claims of innocence ring hollow? How can we be reasonably
certain that she intended -- designed, if you will -- to kill Smith?
We have moved to the last decision node, SP/sp. Confronting us is an event of
small probability (SP): the likelihood that Smith's pacemaker failure was caused
by anything but intense microwave radiation is vanishingly remote. This was
determined at the autopsy before the inquest began: indeed, this finding caused
us to suspect foul play, and thus to begin the inquest. Note, however, that this
small probability event alone isn't sufficient grounds for us to infer design
(i.e., purposeful action) or to implicate Jane Doe. After all, Smith might have
owned a poorly insulated microwave oven or tinkered unwisely with microwave
equipment in his workshop.
The seven lines of evidence, however, do implicate Jane Doe. These, taken
jointly, are what Dembski calls a specification. Specification (sp) is "an
extra-probabilistic notion" (in Dembski's words) that, when conjoined with small
probability, provides robust grounds for inferring design. At the third decision
node, when both SP (small probability) and sp (specification) are present, we
may reasonably infer design as the cause of an event E.
It's important, Dembski said, to see how specification and small probability
necessarily work together to lead us to infer design. "Our naive intuition," he
noted, "is that SP events simply don't happen and can be safely ignored." But,
he continued, that can't be right: small probability events happen all the time.
Flip a coin 1000 times, and you will have participated in an SP event with a
probability of 1 in 10300.
But if a stranger approaches you on the street the next day and gives you a
piece of paper with the exact sequence of coin flips (recorded as 1s and 0s)
that you produced in the privacy of your study, you're entitled to suspect some
funny business. That stranger gave you a specification, and its match with the
SP event you independently produced calls for an explanation. As Dembski put it,
If a probabilistic setup, like tossing a coin 1000 times, entails that some SP
event will occur, then necessarily some extremely improbable event will occur.
If, however, independently of the event we are able to specify it, then we
have cause for surprise and alarm. It's the specified SP events that cannot be
attributed to chance.
In the Smith/Doe case the match is between the SP event itself (microwave damage
to Smith's pacemaker, causing his death) and the seven lines of evidence that
jointly constitute a specification of the event. Note that we could have started
our investigation with one or another aspect of the specification, e.g., the
witnesses placing Jane Doe at the house, and only later -- as evidence
accumulated -- examined the pacemaker for microwave damage. The temporal
relation in our knowledge of the small probability event and the specification
is not important. It's the match between them that convinces us of design and
eventually lands Jane Doe in prison for first degree murder.
This hypothetical example may seem somewhat fanciful. But, as Dembski pointed
out, inferences with exactly this logical structure (i.e., following this
"standard operating procedure") are routinely employed not only by detectives
but also by:
Copyright and patent offices to identify theft of intellectual property
Insurance companies to prevent themselves from being defrauded
Skeptics to debunk the claims of parapsychology experiments
Scientists to identify cases of data falsification
The NASA SETI program to identify the presence of extraterrestrial
intelligence
In other words, we derive and place great weight on design inferences all the
time.
Solving Scientific Mysteries?
Still, Dembski asked, "Is what's good enough for a court of law good enough for
science?" Some worries come crowding in:
Even if one grants that the flow chart accurately describes the pre-theoretic
practice of nonscientists in making design inferences, it's not clear that
this descriptive account should be in any way normative for the practice of
science . . . doesn't design . . . always leave us open to a God-of-the-gaps
objection? And since design does not figure into contemporary scientific
practice, why not rather dispense with it, and concentrate on the
bread-and-butter explanations of science, to wit, chance and necessity?
Flow charts are all very well, but can we be certain that design inferences are
valid? "It turns out," said Dembski, "that a valid deductive argument does
indeed undergird the standard operating procedure that people use to infer
design." The argument may be expressed as follows:
The Argument to Design
Premise 1: E is specified.
Premise 2: E has occurred.
Premise 3: E has occurred either by chance, necessity, or design.
Premise 4: E did not occur by necessity.
Premise 5: If E occurred by chance, then E has probability less than or equal to p.
Premise 6: Specified events of probability less than or equal to p do not occur
by chance.
Conclusion: E occurred by design.
Suppose E, said Dembski, "is the event of opening a safe." We've satisfied
Premise 1: E is clearly specified, because "the safe is so constituted that only
one of the many possible combinations opens it." Premise 2 says simply that E
has occurred. Premise 3, a trichotomy rule, says that E is due either to chance,
necessity, or design. Since most of contemporary science restricts itself to
chance and necessity, Premise 3 at worst introduces a superfluous element,
namely design.
Premise 4 tells us the safe did not open by necessity, which is not
controversial. "No known regularities of nature," said Dembski, "account for the
opening of safes with secure combination locks." Premise 5 is likewise not
controversial. "On any reasonable lock, the probability of hitting the right
combination 'by chance' will be exceedingly small."
Premise 6 is what Dembski calls The Law of Small Probability. This law, he
argued, "is a basic regulative principle of statistics," by which "we are
entitled to eliminate chance as an explanation."
Without this law, he stressed, we are powerless to make judgments in the face of
uncertainty. In particular, statistical inference --which is indispensable to
science -- would be impossible without the Law of Small Probability.
In sum, when applied to the opening of a safe, these premises are unquestionably
true. Since they entail the conclusion, the argument is valid, and therefore the
conclusion itself must be true. The safe was opened by design. (Even if we are
not absolutely certain of the premises, Dembski noted, we can still have
confidence in the argument. "Entailment automatically gives us partial
entailment as well." Thus, if we hold only that the premises are very likely,
the conclusion will itself be very likely.)
Which Premise Do Evolutionists Reject?
The argument to design hides no logical surprises. Yet in the literature of
evolutionary biology, and the many volumes of the creation/evolution
controversy, authors appeal regularly to probability considerations, exhibiting
in addition an intuitive grasp of the notion of specification -- but come to
very different conclusions in the end. Richard Dawkins, for instance, is quite
eloquent on the extraordinary specificity of organisms, and the vanishingly
small likelihood that such specificity could arise by chance. Nevertheless, he
denies that organisms are designed. For Dawkins, organisms are the products "of
purposeless natural forces not guided by any intelligence."
Which premise of the Argument to Design, Dembski asked, does Dawkins reject?
Suppose that the event E to be explained is the occurrence of life here on earth
(call this LIFE). Running through the premises individually, it is clear that
neither 1 nor 2 is problematical for Dawkins (who has written in The Blind
Watchmaker [BW] that organisms "have some quality, specifiable in advance, that
is highly unlikely to have been acquired by random chance alone"). Nor is
Premise 6 a problem. In BW Dawkins sets an upper bound to the "amount of luck"
one is allowed to postulate for LIFE, "clearly restating," Dembski pointed out,
"the Law of Small Probability." Lastly, although Dawkins would regard design as
superfluous in the post-Darwinian scientific world, he plainly sees it as an
empirical possibility. The trichotomy of Premise 3 is safe as well.
Whether Dawkins thinks LIFE is necessary (Premise 4) is, Dembski observed, less
clear, because Dawkins "never assigns precise probabilities to events connected
with the origin of life." Still, it seems reasonable to think that Dawkins would
accept Premise 4, given that his goal in BW is to show that the naturalistic
occurrence of LIFE is probable enough, not that the probability of its
occurrence approaches unity.
Premise 5 is the real focus of disagreement. "Dawkins explicitly rejects Premise
5," said Dembski, by his "appeal to cumulative selection." Dawkins sees
selection over many generations as rendering probable what we would otherwise
naively regard as improbable. It was Darwin's genius, on this view, to provide
the mechanism of selection as a naturalistic means for generating the complexity
of living things.
As an empirical matter, however (Dembski continued), the status of Premise 5 "is
still wide open." It is far from clear that selective mechanisms will suffice to
account for LIFE. How does one go about determining the probability of LIFE? Are
the extant evolutionary scenarios really plausible? Some evolutionists, perhaps
recognizing that probabilistic difficulties have carried off the plausibility of
their scenarios, avail themselves of a cosmological buffet, where they fill
their plates with hypothetical planets and universes in which LIFE may have
arisen -- thus making LIFE on this planet less surprising. As Dembksi put it,
Dawkins, to explain LIFE apart from a designer, not only gives himself all the
time Darwin ever wanted, but also helps himself to all the conceivable planets
there might be in the observable universe (note that these are planets he must
posit, since no planets outside our solar system have been observed, nor is
there currently any compelling theory of planetary formation which guarantees
that the observable universe is populated with planets). Thus Barrow and
Tipler, in order to justify their various anthropic principles, not only give
themselves all the time and planets that Dawkins ever wanted, but also help
themselves to a generous serving of universes (universes which are per
definitionem causally inaccessible to us).
The truth of design, Dembski concluded, is an empirical question to be settled
by looking to nature. Here the philosopher must pass the problem to the
scientist, for the "laws and regularities" involved in Premise 4, and the
"concrete probabilities" of Premise 5, are matters of fact to be determined by
observation and experiment. But scientists should know that the theory of design
leaves the hands of the philosopher marked, as Bertrand Russell said,
... by no formal logical defect; its premises are empirical, and its
conclusion professes to be reached in accordance with the usual canons of
empirical inference. The question whether it is to be accepted turns,
therefore, not on general metaphysical questions, but on comparatively
detailed considerations.4
Those "considerations" are empirical. From Dembski's perspective, the empirical
details speak unmistakably of design; but we should turn to the next speaker,
Michael Behe, who addressed that topic.
Michael Behe (Ph.D., Biochemistry, University of Pennsylvania, 1978) is an
Associate Professor in the Department of Chemistry at Lehigh University. Behe's
research focuses on the structure of nucleic acids -- specifically, working
under a grant from the National Institutes of Health, he examines the structural
properties of certain tracts in eukaryotic DNA to determine their ability to
interact with histone proteins to form nucleosomes, the basic structures of
chromatin (the material found in chromosomes).
While Dembski's talk concerned the logical structure of the design inference,
Behe addressed the biological evidence that (when fitted into the design
inference) motivates many to reject neo-Darwinism in favor of design. "It will
be the burden of my talk," he said, "to show that Darwinism has been unable to
account for phenomena uncovered by the efforts of modern biochemistry during the
second half of this century."
Behe's principal target was the theory of natural selection:
Natural selection, at some level, is the putative engine which pulls the
neo-Darwinian train, and if natural selection stalls, then the whole Darwinian
scheme grinds to a halt.
The data of biochemistry place grave obstacles in the path of neo-Darwinian
explanation by natural selection, Behe stressed, because those data appear to
indicate that, "at its most fundamental level," life is "irreducibly complex."
In the face of such complexity, selection can effect nothing.
Organisms as Black Boxes
As a first step on the path to the notion of irreducible complexity, Behe began
with Darwin's discussion of the evolution of the eye. "How a nerve comes to be
sensitive to light," said Darwin in the Origin, "hardly concerns us more than
how life itself first originated."5 Darwin could lay such questions of mechanism
aside, given the rudimentary biochemical science of his day, and concentrate his
attention instead on finding a series of graded intermediates between the
simplest and most complex eyes, arguing that selection sufficed to bridge the
differences. The less that is known about how eyes (or other complex structures)
actually work, Behe noted, the easier this strategy of evolutionary explanation.
One simply strings together a series of black boxes.
"Unconstrained by knowledge of the mechanism," he said, we find it easy "to
imagine simple steps leading from nonfunction to function." Calvin and Hobbes
can easily imagine that the cardboard box into which they have climbed might
take them into the air. Adults, on the other hand, know that a cardboard box is
no more likely to fly than a pile of stones. Human powered flight occurs via
complex mechanisms, and the "black box" of an airplane is black only to those
(most of us) who know nothing about aeronautics and avionics. Analogously, Behe
continued,
... when the exploratory vessel H.M.S. Cyclops dredged up some curious-looking
mud from the sea bottom, no less a personage than Thomas Henry Huxley became
convinced that it was Urschleim
... the progenitor of life itself, and Huxley named the mud Bathybius
Haeckelii, after the eminent proponent of abiogenesis (German evolutionist
Ernst Haeckel).
Haeckel and Huxley, seeing single-celled living things as "simple," could regard
Bathybius (an artifact caused by the alcohol used to preserve the dredged mud)
as their evolutionary precursor. As the real complexity of even the simplest
organisms became apparent, however, "belief in spontaneous generation faded
away."
The mistaken perception that single-celled organisms were "simple" was abetted
by their status as black boxes. But just as modern biochemistry has "opened the
black boxes of many biological systems," said Behe, and elucidated at the
molecular level such functions as vision, so our understanding of what it means
to explain biologically should likewise shift, to take account of what we now
know.
Proteins
"Proteins," said Behe, "are the machinery of living tissue that build the
structures and carry out the chemical reactions necessary for life." Much like
the carpenter's workshop that contains many different types of tools for various
tasks, so "a typical cell contains thousands and thousands of different types of
proteins," to carry out the diversity of functions that sustain life. Assembled
from amino acids in chains "anywhere from 50 to 1,000 amino acids" long,
proteins fold up into "very precise" three-dimensional structures -- and those
structures determine their precise functions.
Protein structure and function are therefore as fundamentally linked as the
structure and function of the tools in the carpenter's shop. Like the tools,
said Behe, "if the shapes of the proteins are significantly warped, then they
fail to do their jobs."
But how much "warping" can a protein tolerate? asked Behe. The three-dimensional
structure of a protein is determined by its primary sequence. A change in that
primary sequence, from a positively to a negatively charged amino acid, for
instance, may affect the protein's ability to fold properly, and hence its
function. In a small protein of, say, 100 amino acid residues, there are 20
possible amino acids for each site. Thus, the probability of finding the right
amino acid for the first site is 1 in 20. The probability of finding the correct
two amino acids, in the first and second positions, is 1 in 20100, and so on.
For the entire protein, the probability would be 1 in 20 to the one hundredth
power (or 10130).
Yet it has long been known, Behe continued, that similar proteins from different
species show differences in their primary amino acid sequences, while still
folding to "closely similar structures." It is possible, therefore, "for two
different but similar amino acid sequences to be structurally and functionally
equivalent." Some amino acid changes appear to be tolerated. Is there a limit,
however, to what changes are possible? And is there a way of answering that
question directly (rather than only comparatively)?
At MIT, in the laboratory of Robert Sauer and his colleagues, just such a direct
answer was sought for several viral proteins. Taking the genes for the viral
proteins, Sauer's group systematically deleted small pieces (corresponding to
the instructions for three amino acids at a time), and inserted altered pieces
back into the genes at the sites of the deletions. The altered genes, placed in
bacteria, produced altered proteins. Since the bacteria quickly destroy proteins
which fail to fold properly, Sauer's group was able to isolate the altered
proteins that were not destroyed. By sequencing those altered proteins, the
biologists could observe which amino acids, in which positions, would produce a
folded, functional protein.
What Sauer's group found, said Behe, was that some sites tolerated a great
diversity of possible amino acids (up to 15 out of 20 possibilities). Other
sites tolerated much less diversity: only three or four amino acids would still
yield a functional protein. Other sites, however, had "an absolute requirement
for a particular amino acid" --no substitutions would work:
This means that if, say, a P does not appear at position 78 of a given
protein, the protein will not fold regardless of the proximity of the rest of
the sequence to the natural protein.
Gathering these experimental results over the whole length of the protein, one
can readily calculate the likelihood of finding a folded protein by a random
mutational search: about 1 in 10 to the 65th power. The number, Behe noted, is
"virtually identical to results obtained earlier by theoretical calculations," a
confirmation that "greatly increases our confidence that a correct result has
been obtained."
Molecular Machines
As "complex and improbable as folded proteins are," said Behe, "in many
biological structures [they] are simply components of larger molecular
machines." In these larger structures, each protein component functions only
"when all of the components have been assembled."
Consider, Behe observed, the molecular machine of a cilium. Cilia are
microscopic hair-like organelles found on the surfaces of many cells, that, by
beating in synchrony, move fluid over the cell's surface, or propel single cells
through a fluid. The epithelial cells lining the human respiratory tract, for
instance, each have 200 cilia moving synchronously to sweep mucus (bearing
foreign particles) towards the throat, where it can be eliminated.
The major protein components of a cilium can be seen in the top-down cross
section of Figure 2.The ciliary core, or axoneme, is a plasma membrane-coated
bundle of fibers, which includes a ring of 9 double microtubules, surrounding 2
central single microtubules (the "9 + 2" array). Each outer doublet is composed
of 13 filaments (A subfibers), fused to an assembly of 10 filaments (B
subfibers). The individual filaments are themselves composed of two proteins
called alpha- and beta-tubulin.
The 11 microtubules forming an axoneme in the "9 + 2" array are held together by
three types of connectors (see Figure 2):
1. The A subfibers are joined to the central microtubules by radial spokes,
which terminate in a knoblike feature called a spoke head.
2. Adjacent outer doublets are joined by linkers along the circumference, that
consist in part of a highly elastic protein called nexin.
3. The central microtubules are joined by a connecting bridge. Each type of
connector is repeated along the length of the axoneme with its own
characteristic periodicity.
Finally, every A subfiber has two arms -- an inner arm and an outer arm -- both
containing the protein dynein.
So, asked Behe, "how does a cilium work?" Experiments have shown that ciliary
motion is caused by the chemically-powered "walking" of the dynein arms along
the adjacent B subfibers. (See the side view cross section of an axoneme segment
in Figure 3.) Using ATP -- the common carrier of cellular chemical energy -- as
their power source, the dynein arms on one microtubule "walk" up the neighboring
B subfiber of a second microtubule, so that the two microtubules slide past each
other.
This sliding motion is transformed into a bending motion by the nexin protein
cross-links. The nexin cross-links keep the neighboring microtubules from
sliding past each other by more than a short distance, thereby converting the
dynein-induced sliding motion into a bending motion of the entire axoneme.
What happens to the bending function of the cilium, however, if its components
are removed experimentally one by one? Remove the dynein arms, said Behe, and
the cilium becomes rigid and inflexible. Its flexibility can be restored only
when the dynein is replaced. Remove the nexin cross-links (by exposing them to
the proteolytic enzyme trypsin), and the microtubule doublets slide past each
other without stopping. The axoneme simply falls apart. Remove the alpha-and
beta-tubulins, and there will be no filaments at all to bend. Removing one or
another of the ciliary proteins, concluded Behe, "is like trying to design a
pulley without a rope, or a lever without a fulcrum." Each protein has its
proper function only when all are present.6
The cilium, continued Behe, is an example of "irreducible complexity."While
plainly a complex structure, like an eye or a feather, the cilium possesses a
complexity of a remarkable type:
It is also irreducible complexity. By this I mean that the components of the
cilia are not themselves composed. They are single molecules. There are no
more black boxes to invoke: the complexity is final.
The implications of irreducible complexity for the theory of natural selection
are devastating. "Since the complexity of the cilium is irreducible," said Behe,
"it cannot have functional precursors." The evidence at hand seems strongly to
suggest that one either has a cilium, with all its necessary protein components
in place -- or one has nothing (or nothing functional, certainly). There seems
to be no actual or even imaginable gradient of simpler molecular structures
leading up to a cilium. Yet such a gradient is exactly what natural selection
requires. Because the cilium does not have functional precursors, said Behe, "it
cannot be produced by natural selection, which requires a continuum of function
to work. Natural selection is powerless where there is no function to select."
And if the cilium cannot be produced by natural selection, he added, "then the
cilium was designed."
The Burden of Proof and the Study of Molecular Evolution
Darwin himself (Behe continued) set the standard of proof for advocates of the
theory of design in the Origin:
If it could be demonstrated that any complex organ existed, which could not
possibly have been formed by numerous, successive, slight modifications, my
theory would absolutely break down. But I can find no such case.7
Yet, Behe argued, "Examples of irreducible complexity can be found on virtually
every page of a biochemistry textbook." Although the cilium is a striking
example, because of its manifestly mechanical aspects, other such systems
abound:
Other examples of irreducible complexity [include] aspects of blood clotting,
closed circular DNA, electron transport, the bacterial flagellum, telomeres,
photosynthesis, transcription regulation -- virtually any biochemical system.
Where can one go, asked Behe, to find plausible step-by-step Darwinian scenarios
for the origin of these complex systems? "A good place to look for an answer to
that question," he said, "is in the Journal of Molecular Evolution (JME). JME
was started "specifically to deal with the topic of how evolution occurs on the
molecular level." It has high standards and is edited by prominent figures in
the field of molecular evolution.
Yet, to the observer looking for Darwinian explanations, JME can only be
regarded as a great disappointment. Behe tallied the results of the journal's
past 10 years of publication:
JME has published 886 papers. Of these, 95 discussed the chemical synthesis of
molecules necessary for the origin of life, 44 proposed mathematical models to
improve sequence analysis, 20 concerned the evolutionary implications of
current structures, three discussed biochemical properties of current
organisms, and 719 were analyses of protein or polynucleotide sequences. There
were zero papers discussing models for intermediates in the development of
complex biomolecular structures.
"If one looks at other journals or books," he continued, "the story is the
same." Sequence comparisons abound, while models for the actual evolution of
complex systems are hard to find.
"It is important to realize," Behe said, in ending his talk, "that we are not
inferring design from what we do not know, but from what we do know. We are not
inferring design to account for a black box, but to account for an open box."
While we may be shocked to find open boxes speaking plainly of design, he said,
"we must deal with our shock as best we can and go on."
One can imagine that many listeners would find Behe's talk compelling, but, in
the end, intuitively unsatisfying. Such listeners might reason as follows: "To
be sure, the biological world is replete with complex systems, for which we have
no plausible or even sketchy naturalistic explanation. However, it is the
business of science to provide such explanations, and not something else. Where
a natural explanation is lacking, we place the problem on a shelf, marking it
'unsolved,' and if it gathers dust there, so be it. Science traffics, after all,
in the empirical. What philosophers or theologians care to do is their business.
But don't ask scientists to infer design when that inference goes against all
that their enterprise stands for!"
Behe would doubtless have his own sharp answer to this line of argument. But the
next two speakers, Stephen Meyer of Whitworth College, and Paul Nelson (me),
spoke directly to several variants or conceptual relatives of the argument. I
turn next, then, to Steve Meyer.
Stephen Meyer (Ph.D., History and Philosophy of Science, Cambridge University,
1991) is Assistant Professor of Philosophy at Whitworth College in Spokane,
Washington. Meyer's Cambridge dissertation, on methodological questions in
origin-of-life research, set him to thinking about a number of philosophical
claims that have been used to adjudicate (actually, to dismiss) the intelligent
design explanation for the origin of life.
Those claims hold that there are in principle sound methodological reasons for
refusing to allow design as an explanation for the origin and diversity of life.
However, Meyer contended, after critical examination the soundness of the
reasons dissolves away. There are therefore no compelling philosophical grounds
for excluding design; or, to put it another way, if judged by non-question
begging criteria design is fully as explanatory as any other cause.
Yet, Meyer noted, most biologists are ill-disposed to see design as a genuine
explanation. Their resistance is puzzling, however, in the light of (a) the
persistence of teleological language in biology, and (b) the lack of progress in
the reductionistic, naturalistic research program in the problem of the origin
of life.
Consider the persistence of teleology. As Stanford historian of biology Timothy
Lenoir has noted,
Teleological thinking has been steadfastly resisted by modern biology. And
yet, in nearly every area of research biologists are hard pressed to find
language that does not impute purposiveness to living forms.8
Biological objects, said Meyer, seem designed. And attempts to render the
appearance of design illusory, by showing that it is a necessary consequence of
natural laws acting at lower levels, have been less than successful. Resistance
to design as an explanation cannot stem, for instance, from the achievements of
the naturalistic thrust in origin-of-life research.
One of Meyer's own dissertation advisors, an expert in the origin-of-life field,
noted to Steve in 1989 (after returning from an international con-ference on the
topic, in Prague) that the question "How did life arise naturalistically?" had
in recent years acquired the potential to become a spawning ground for
scientific cranks -- so little was the field united by any one or even small
number of generally accepted theories. Francis Crick's agnosticism on the same
subject is well-known:
An honest man, armed with all the knowledge available to us now, could only
state that in some sense, the origin of life appears at the moment to be
almost a miracle, so many are the conditions which would have had to be
satisfied to get it going.9
Klaus Dose, another expert in the field, found little cheer in the fruits of the
last few decades:
More than 30 years of experimentation on the origin of life in the fields of
chemical and molecular evolution have led to a better perception of the
immensity of the problem of the origin of life on Earth rather than to its
solution. At present all discussions on principal theories and experiments in
the field end either in stalemate or in a confession of ignorance.10
Other such sentiments have been widely expressed.
Why Exclude Design as an Explanation?
"Why then the expectation," asked Meyer, "that we will find the answer to the
question in naturalistic terms?" Why no consideration, whatsoever, for the
possibility of a scientific theory of intelligent design?
"For most scientists," he continued, "there is a perception that the 'rules of
science' forbid those types of inferences -- that is, inferences to a
pre-existent intelligence." Philosopher of science Nancy Murphey casts the issue
in terms of what she thinks science itself seeks, namely, naturalistic
explanations for all natural processes. "Christians and atheists alike," Meyer
quoted Murphey as arguing, "must pursue scientific questions in our era without
invoking a creator." Any reference to a creator ipso facto leaves the realm of
science and enters that of metaphysics and theology.
"This is the answer to our question," said Meyer. "Our era is one which
proscribes the possibility, which outlaws the possibility of talking about
creative intelligence as an explanatory entity within science." But when exactly
did this proscription arise? Nancy Murphey, noted Meyer, admitted that the
naturalistic definition of science has dominated for only about 130 years. "It's
historically contingent," he continued. "Most of biology prior to Darwin was in
a creationist framework. Newton and Boyle, during the period of the Scientific
Revolution, were quite fond of making design arguments, and not just on the
basis of biology, but in optics and astronomy as well."
The issue can be framed as the "categorical opposition" of the philosophical
doctrine of methodological naturalism versus intelligent design. Methodological
naturalism simply does not admit the possibility of intelligent design. One can
accept the theory of intelligent design, of course, but not as a scientific
proposition. "Or, as I've heard many times," joked Meyer, "it might be true, but
it can't be science."
But is methodological naturalism, asked Meyer, "purely an arbitrary convention?"
If so, some people may no longer feel themselves bound by it. On the other hand,
if good reasons ground methodological naturalism, "perhaps the 'rules of
science' ought to continue as they are."
Demarcation Arguments as 'Litmus Tests' for Scientific Standing
The ASA, Meyer noted, "tends to defer to methodological naturalism as a
convention, on the basis of 'what science does.' Our secular colleagues,
however," he continued, "do attempt to justify the convention," offering
arguments for a purely naturalistic science. Within the philosophy of science
proper, such arguments are generally called demarcation arguments. Demarcation
arguments attempt to distinguish "true science" from all other human activities,
in particular, from "pseudoscience, metaphysics, religion -- and other bad
things of that sort." Although "that may sound facetious," Meyer continued,
"there's an attempt for a distinction of epistemic value or epistemic warrant,
on the basis of some philosophical litmus test." For example, a truly scientific
theory must be falsifiable, testable, and explain by reference to natural law.
These are all examples of criteria that (putatively) distinguish true science
from pseudoscience.
"Now the main rap on intelligent design," said Meyer, "is first of all that it's
not naturalistic." But methodological naturalism comes into play because design
allegedly fails to meet the standard demarcation criteria: it's not testable,
doesn't explain by reference to natural law, it's unobservable -- "you can't put
God in a test tube and study Him." Demarcation arguments of this sort are
regularly given as reasons for completely rejecting design as a possible
explanation.
But within the philosophy of science, "demarcation arguments have totally
failed." This is a general judgment, said Meyer, that can be nicely illustrated
by a particular case. One of the things that emerged from the 1981 Arkansas
"equal time" (creation/evolution) trial was the ACLU's skill at persuading the
late Federal judge William Overton to accept its construal of the philosophy of
science. The philosophy of science promulgated by the ACLU excluded young-earth
creationism as being in principle nonscientific; creationism was trapped
philosophically under the demarcation arguments offered by expert witness
Michael Ruse.
Yet, in the wake of the trial, Ruse's arguments were widely criticized in the
philosophical community, Meyer noted, as "setting the philosophy of science back
50 years." Ruse's arguments were assembled from a "simplistic" logical
positivism and the neo-positivism of Sir Karl Popper. The trial then became a
contest of "Popper versus Popper," as the creationists themselves assumed the
soundness of Popperian neo-positivism. Ruse and the ACLU simply did a better job
of persuading Overton that they, rather than the creationists, were the true
Popperians.
Popper has been important in the development of the philosophy of science,
allowed Meyer. But even after we give him his full due, we must face the charge
that Popper's philosophical theories fail to correspond with the way science
actually functions. "Ruse, who ought to have known better in the early 80s,"
said Meyer, "put forward a definition of science that neither evolutionary
theory nor intelligent design could meet. Therefore there is already culturally
something fishy going on with demarcation arguments." Citing the philosophers
Martin Eger and Larry Laudan, Meyer noted that demarcation arguments -- although
known to be deeply flawed by professional philosophers of science -- continue to
play a role in disputes like the creation/evolution controversy, or discussion
of design.
The list of demarcation arguments against design offered in the scientific
literature is long. Intelligent design held not to be scientific because (among
other things):
1. It does not explain by natural law
2. It invokes unobservables
3. It is not testable
4. It does not make predictions
5. It is not falsifiable
6. It provides no mechanisms
"And on and on," said Meyer, adding that he is currently looking for all such
arguments, with a standing request to those interested that any demarcation
argument not already mentioned be sent to him for his exhaustive catalogue.
When demarcation arguments are applied in origins research (comprising all types
of evolutionary theory and all types of intelligent design theory), "one of two
things obtain," Meyer said.
Either the arguments are applied in so narrow a way as to exclude both
naturalistic descent with modification and intelligent design, or they are
applied in a more liberal, loose way, and both intelligent design and
naturalistic descent must be included within science. Either they exclude
both, if they are applied consistently, or they include both.
"These are not scientific arguments," stressed Meyer, "although you usually hear
scientists making them. These are not arguments about nature. These are
arguments coming out of the philosophy of science -- actually, very bad
philosophy of science."
Whether organisms evolved by natural means from a common ancestor, or were
designed, is a factual question to be settled by the evidence, Meyer urged, not
by a priori philosophical arguments. "In some ways what I'd like to do," he
added, "is to put my own profession, the philosophy of science, out of
business," at least where the question of the history of life is concerned.
Legitimate factual questions are being "adjudicated by philosophical and
methodological litmus tests, not by the evidence itself."
The Criterion of Explanation in Terms of Natural Law
The litmus tests fail when looked at closely. Consider the criterion of
explanation solely in terms of natural law, offered most prominently in the
creation/evolution dispute by the philosopher and historian of biology Michael
Ruse. On Ruse's construal of natural law, said Meyer, "everything else follow
from that -- falsifiability, testability, prediction, repeatability -- all these
things follow from science's reliance on natural law." No theory of creation or
intelligent design, however, explains by reference to natural law; hence, no
theory of design can be scientific.
However, many areas of natural science do not explain solely by natural laws,
but rather explain by referring to past events. In many of the historical
sciences, as in forensic inquiry (e.g., criminal detective methods), the main
explanatory work is done by a reconstructive scenario that, by postulating an
event or series of events, attempts to link as many of the relevant facts or
circumstances as possible. One begins with a set of facts and infers into the
past to the event (or events) that would best explain those facts.
Darwin's theory of common descent, for instance, "attempts to infer from things
we can see," said Meyer, "back to an unobservable causal history. ... What's
doing the explanatory work for Darwin is the assertion that certain events --
unobservable transitional intermediates, if you will, in the fossil record --
would explain what we see in the present." While natural laws may play a
background role in our assumptions, historical explanations (in evolutionary
theory, for instance) would not work without the key events they postulate.
There is a direct parallel here to the theory of design, which postulates the
past action (i.e., event) of a mind acting on matter. But if explanations in
terms of past events are inadmissible, design will be "ruled out of court," said
Meyer, "which is exactly what happened." Yet there seems to be no good reason to
exclude past events as explanations, especially since in practice "we explain by
individual past events all the time."
The Criterion of Observability
"Ruse's argument," concluded Meyer, "does not take into account the actual
diversity of methods in science, or in the historical sciences in particular."
Other demarcation arguments fare no better. It is often claimed, for instance,
that "God" cannot be an explanatory term because it describes an unobservable
entity -- and science deals only with observables. "But if observation is the
hallmark of testability," said Meyer, "an awful lot of things in science would
be out of court." In a symposium at SMU in March 1992, the molecular biologist
Fred Grinnell argued that anything which cannot be measured, counted, or put in
a test tube -- in other words, directly observed --simply cannot be invoked in a
scientific explanation. "I asked Grinnell," said Meyer, "if he accepted the
double-helical structure of DNA, or many of the other inferred entities in
molecular biology." Science is rife with unobservables. Physics, geology, and
other sciences regularly employ them: "We infer from what we can see to what we
can't see." Darwinism, for example, refers to biological events in an
unobservable past.
"But if observability is a necessary condition for being scientific," said
Meyer, "then the Darwinian theory doesn't qualify as science either." Make the
criterion of observability more liberal, and "you save the scientific status of
Darwinism. But you also let design in as well."
"Again and again when I examined these arguments," said Meyer, "I found that
they do not discriminate." Applied rigorously and neutrally, the arguments
failed to exclude design without also excluding Darwinian descent. Applied
liberally, the arguments allowed both design and descent. One could of course
simply stipulate that "we want only to look at naturalistic theories" (in which
case demarcation arguments, if offered as objective philosophical criteria, are
in fact so much window-dressing to flummox the unsophisticated). But if one
assumes a position of genuine neutrality, demarcation arguments wield a
philosophical scythe that indiscriminately mows down all lines of origins
research -- Darwinian and design-based.
A Good Reason to Include Design
There is, however, at least one good reason to include design as a proper
explanation. Meyer's own research in the philosophy of science was on the
methods of the historical sciences. "There is more than one scientific method,"
he said. "In fact there are at least two." The inductive sciences (by which we
might understand physics, chemistry, and the other primarily experimental
sciences) are motivated by the question "How does nature normally operate?" The
historical sciences (by which we might understand cosmology, geology,
paleontology, evolutionary theory and biological systematics), on the other
hand, are motivated primarily by the question "How did this system or object
come to be?" These are logically distinct questions. In the latter case, when we
ask how something came to be, we explain by invoking causal narratives or
patterns of events -- employing methods often termed "abductive" or
"retroductive" -- to find that set of events that best accounts for the features
of what we observe in the present.
This is "detective-style reasoning," said Meyer, and while such reasoning
certainly employs natural laws (the bread-and-butter of the inductive or
experimental sciences), those laws are insufficient tools for answering the
questions posed in the historical sciences. The point has been appreciated well
by evolutionary theorists defending their domain against the skepticism of their
more experimentally-minded colleagues. In evolutionary theory, says Stephen Jay
Gould, "we infer history from its results."
This means that testing, or theory evaluation more generally, will also differ
in important ways between the inductive and historical sciences. As Darwin often
argued to his correspondents, the theory of common descent by natural selection
had to be weighed comparatively, "vis-a-vis its competitors." Explanations are
judged by their relative power, and by their consistency with what we know from
the present.
"Can a theory of design be formulated to meet these standards?" asked Meyer.
Yes: the theory is attempting to answer a "What happened?" question, and does so
by postulating the past action of an intelligent agent. "That's a perfectly
appropriate answer," he said, "to a perfectly appropriate historical question."
Starting with distinctive features of living systems (as discussed by Michael
Behe, for instance), design attempts to account for those features by referring
them to a sufficient cause, namely, an intelligence. In every respect, argued
Meyer, design as a theory is logically fully consonant with the types of
answers, and methods of evaluation, common to the historical sciences.
Meyer's Conclusion
The origin of life, said Meyer, is a scientific question that cannot be settled
by philosophical gerrymandering or a priori definitions. "It is an empirical
question that must be left fully open to whatever hypotheses come along. There's
nothing within the philosophy of science that justifies the exclusion of
design."
Meyer ended his talk by reiterating those features of living systems he regarded
as explicable only by design: the conjunction of small probability and
specification, the existence of coded information, and the complex functional
interdependence of the components of organisms.
"The 'logic boards' of living things," said Meyer, "are best explained by
design." Yet the doctrine of methodological naturalism stands in the way of our
using the theory. We need to end "this hear-no-evil, see-no-design" outlook,
urged Meyer, for the good of science.
I turn next to my talk -- the last of the symposium.
For simplicity's sake, I shall refer to myself in the first person, and ask the
reader's indulgence for the informality. I am a Ph.D. candidate in Philosophy at
the University of Chicago, where I also studied evolutionary theory and
systematics. My dissertation treats the conceptual relationship of the theory of
common descent to theories about the causal structure of animal development.
It fell to me, by the request of the symposium organizers, to answer the
question of how a theory of design might be practically applied by working
biologists. But this question is, in a sense, premature. A well-articulated
theory of design is not yet at hand. Indeed, it may be some time before such a
theory is available for direct application in the day-to-day work of biologists.
But we can pose the question in a slightly different form. If a scientist who
implicitly or explicitly accepted methodological naturalism were to lay that
doctrine aside, and take the possibility of design seriously, How would his or
her scientific practice differ? Would it differ?
This question is best answered by considering perhaps the most important
standing objection to design, one that (I think) reflects a profound antipathy
to the theory throughout modern science and the philosophy of science. I refer
of course to the "God-of-the-gaps" objection, which is taken to show design's
theoretical bankruptcy and hence its uselessness for the real work of scientific
explanation. If this objection cannot be turned back, design will never gain a
hearing among its skeptics.
As it turns out, however, the God-of-the-gaps objection is entirely generic.
That is, the objection is an epistemological difficulty that actually inflicts
all scientific theories -- and therefore counts specially against none.
The Explanatory Mosaic
We might put the God-of-the-gaps objection as follows. Design, its critics
argue, suggests no research of its own, and provides no answers other than the
vacuous. Rather, design is parasitic on what Elliott Sober calls "the
incompleteness of science."
Let me illustrate what I mean by "parasitic" with a simple visual metaphor.
Figure 4 depicts what I shall call "The Explanatory Mosaic."
Now this is a conceptual, not physical, space. Its boundaries are set by a
question I suppose pretty much all of us want answered, namely, "How did the
biological world come to be?" By "the biological world," I mean everything one
might imagine falling under that phrase: the first origin(s) of life, the
origins of the major groups of plants and animals, the origins of the complex
molecular structures presented by Behe, and so on -- right down to the origin of
human consciousness.
We should note a couple of things about the Explanatory Mosaic. First, many
people are working on it, over a really vast theoretical and empirical area.
Most of the people have no (or only very indirect) contact with each other. But,
they are working on one or another aspect of the same problem ("How did the
biological world come to be?"). Thus, if we're going to have a coherent answer
when the mosaic is complete -- in other words, if we're going to have a
filled-out pattern that makes sense -- we're going to need a theory (a picture)
to guide our work. It's the theory that tells us what tiles go where in this
vast space.
Secondly, work on the mosaic may proceed episodically and locally. In some
locations, the tiles may fall rapidly and easily into place; while in other
locations, the work may move slowly, or not at all. Indeed, tiles once thought
firmly situated may have to be torn out, so that a once-unified part of the
mosaic returns to a heap of unsolved puzzles. There's no guarantee that local
explanatory progress translates into progress elsewhere.
By the consensus of the scientific community, neo-Darwinism (understood as the
common descent of all organisms from a single ancestor, by means of variation
and selection) has nicely filled in many parts of the mosaic.Work is proceeding
with this general picture, as a guiding schema, very much in mind. We needn't
haggle over what percentage of the area has been filled in according to the
neo-Darwinian picture (we needn't take the metaphor that seriously), but most
observers think some progress has been made. We can represent those areas by the
crosshatched parts of Figure 4.
Problems With Filling in the Evolutionary Picture
Yet, unsolved problems remain. While evolutionists have a general idea of what
the final mosaic will be, that is, the common descent of all organisms with a
central role for natural selection as the process theory, they don't know much
about the details. And, over the past two decades there has been a rising level
of discontent within neo-Darwinism about the sufficiency or even necessity of
it. Consider some recent expressions of unhappiness. From geneticist Martin
Kreitman:
Many of the simplest and most com- mon patterns of morphological evolution
still elude satisfactory explanation. In a recent conversation, Richard
Lewontin pointed out to me that many morphological characters are essentially
invariant within species -- the scutellar bristle number and position in
Drosophila, for example -- but are manifestly different between species. The
"whole problem of evolution," according to him, is to explain this seeming
contradiction. Why, he wanted to know, do characters like that exist?11
From developmental biologist Wallace Arthur:
One can argue that there is no direct evidence for a Darwinian origin of a
body plan -- black Biston betularia [peppered moths] certainly do not
constitute one! Thus in the end we have to admit that we do not really know
how body plans originate.12
From geneticists Bernard John and George Miklos:
As unpalatable as it may seem to many biologists, certain aspects of
conventional evolutionary theory have become stalled, and it is futile to
pretend that continuing study along the well-worn, mathematically oriented
neo-Darwinian pathways will provide significant insights into key evolutionary
phenomena.13
And so on. Other such worries can escalate into disenchantment even with the
theory of common descent, but that would take us too far afield. The point is
that large numbers of evolutionary theorists think neo-Darwinism has ceased to
work as the picture (if you will) that guides their labor.
Sure, the theory handles certain phenomena well, but on the really big
questions, such as the origins of the major groups, or of complex structures,
there is a diminishing conviction that neo-Darwinism is up to the task. And as
we take in the whole mosaic, of course, to include such problems as the origin
of life, neo-Darwinism is plainly insufficient (or inapplicable).
Do Design Explanations Depend on the Incompleteness of Science?
So what does the design theorist do -- according to the God-of-the-gaps
objection -- when he comes upon the incomplete Explanatory Mosaic? He surveys
the open areas, i.e., the unsolved problems, and wherever they exist lays down a
quick, easy, uniform veneer of design. (See Figure 5, area filled by vertical
lines.) Do you have an unsolved problem? It's no problem: God did it. The theory
of design must be true. Look at all these unsolved problems and open areas the
theory so readily and completely fills!
Here's how Elliott Sober puts the design theorist's move:
This argument begins with the fact that there are many features of the living
world that evolutionary theory cannot now explain. The origin of life, for
instance, remains an active area of scientific research. ... Science is shot
through with ignorance. Doesn't this provide an opportunity for creationist
explanations to be pressed home?14
But, Sober continues, this doesn't follow:
Our current ignorance is no evidence for the truth of any explanation,
creationist or otherwise. The fact that we currently do not understand various
facts about life is no reason to think that God has intervened in life's
history.15
Why not? The answer can be seen by looking at Figure 5. Suppose the crosshatched
area in the lower left-hand corner of the mosaic were to expand a bit. Research
reveals new evolutionary mechanisms, and thus resolves a long-standing problem
in, say, the adaptive modification of mammalian limbs. As that area expands, the
area occupied by the design theory necessarily shrinks.
But if design's area can shrink, then nothing was there in the first place. If
we imagine that, in Figure 5, the design tiles (the vertical lines) were
genuinely occupying explanatory space, then evolutionary theory couldn't expand
into the space occupied by design. That would be geometrically impossible, the
plane (within the boundaries set by the question) having been completely tiled.
But (on the objection we're considering) the area occupied by design necessarily
shrinks as evolution expands. Thus, the explanatory content of design is
governed entirely by whatever problems happen to be unsolved by evolutionary
theory. As Sober puts it,
Creationists try to parlay the current incompleteness of scientific knowledge
into points in their favor. ... We can expect creationists in the future to
choose a different array of phenomena since many of the problems that
currently puzzle science probably will be sorted out in the future.16
Here we might press the question of why (on this objection) design has no
content, and necessarily retreats before the advance of evolution. The usual
answer says that the principal cause of design theory -- an omnipotent,
invisible deity -- is utterly inscrutable. Moreover, an inscrutable cause can be
invoked at will, wherever one pleases:
In its ultimate extension, [the design hypothesis] represents what might be
termed the 'Will of Allah' point of view: whatever happens is God's choice.
Putting it the other way around, God's choice is whatever happens, and this
means that a divinity can always be invoked without the possibility of
challenge.17
Scientists do not think they now have all the answers. That is why they
continue to do research. On the other hand, creationists have at hand an
all-purpose explanation for any observation you please. The origin of life,
the distribution of modes of reproduction, and everything else can be
explained by a four-word hypothesis: "It was God's will."18
In general, the God-of-the-gaps objection holds that unsolved problems are only
that: unsolved problems. Design is parasitic because it rides like a conceptual
remora on the back of the prevailing naturalistic theory, drawing whatever
content it has from the shortcomings of that theory. As those shortcomings are
resolved, design is correspondingly diminished. Sober nicely expresses this
intuition, which motivates the God-of-the-gaps objection. "The past successes of
scientific explanation," he writes, "suggest that was is now inexplicable may
eventually be brought within the scope of scientific understanding."19
This objection has long troubled me, and I have here tried to express it as
forcefully as possible. How should it be answered?
What are the "Gaps" in the Phrase "God of the Gaps"?
We might start by looking at the very phrase "God-of-the-gaps." To what does the
word "gap" here refer? Is the gap in the world, among the phenomena? Of course
not. The gap is given by -- is relative to -- some theory about the phenomena.
The gap exists in our heads (as it were), because a theory has posed a puzzle
for which we do not have an answer: yet the theory also tells us to expect to
find an answer.20
But if the theory we are presupposing is false, then the gap we want to fill, or
the answer we are seeking, may not exist. Let's return to the metaphor of the
mosaic. If we presuppose the truth of naturalistic evolution, then we will set
to work filling the mosaic according to that picture. It's the theory, after
all, that tells us where to lay the tiles, or to try to lay the tiles.
If the tiles won't go into place, however, we have some grounds for thinking
that the theory guiding everyone's work might not be true. If the difficulties
persist, and a pattern of unsolved problems emerges, we might wonder whether
another picture wouldn't do a better job of guiding research. That picture would
dissolve some or perhaps most of the "gaps" (research problems) of the older
picture, by rendering them ill-framed, or nonexistent.
Consider the puzzle of the naturalistic origin of life. This "gap" arises for
evolution because according to that theory the parts must precede the whole:
that is, the nonliving constituents of organisms must be temporally and causally
prior to organisms (first came methane, carbon monox-ide, ammonia, and water;
from these, amino acids; from these, proteins, and so on). Furthermore, only
"natural" causes may be employed in scientific explanation.
But there is nothing in the question, "How did living things come to be?" -- the
question accepted as valid by both evolutionists and non-evolutionists as
setting the boundaries of the mosaic, but not determining its internal patterns
-- that dictates the necessity or truth of either evolutionary assumption.
Indeed, with biological systems, the whole may well precede its parts, and in
the absence of some sound philosophical justification the prohibition against
design as a cause is arbitrary and question-begging.
Looking for a Theory of Design with Positive Content
If we take a design-based theory as our guiding picture, however, the gap
created by the evolutionary puzzle "How did life arise naturalistically?"
wouldn't be so much filled by design as dissolved by it. "How did life arise
naturalistically?" as Kuhn writes of the problems posed by theories generally,
is:
... a puzzle for whose very existence the validity of the paradigm must be
assumed. Failure to achieve a solution discredits only the scientist and not
the theory. Here ... the proverb applies: 'It is a poor carpenter who blames
his tools.'21
It is not a poor carpenter who blames the blueprint, however, when he finds that
it dictates an impossible structure. It is fully rational for a scientist who
recognizes the intractability of his research puzzle to abandon it, if he
discovers that the puzzle presupposes something false. (Indeed it would be
irrational to do otherwise.) It is likewise fully rational for a scientist to
find another puzzle to solve, one posed by a theory grounded on different
principles.
To do so, of course, we carpenters (or scientific mosaic-builders) must have a
theory of design that projectsits own patterns into the space established by the
question, "How did living things come to be?" It would then not be evolutionary
theory telling us what to expect observationally and theoretically, but design
(see Figure 6). Some of the so-called "unsolved problems" of evolutionary theory
might then become design-based predictions, perhaps framed as proscriptions,
that is, as propositions of the form "event or phenomenon x will not occur."
Consider an example. In 1983, the creationist molecular biologist Siegfried
Scherer published a paper in the Journal of Theoretical Biology on the evolution
of light-driven cyclic electron transport, the energy-producing mechanism of
bacterial photosynthesis. He estimated the number of basic functional states
required to evolve "a microorganism with a light-driven cyclic electron
transport process" from "an anaerobic heterotrophic microorganism lacking
membrane-associated electron transport" -- a critical step in the early
evolution of life.
Scherer estimated that no fewer than five new proteins would be needed to move
from "fermentative bacteria, perhaps similar to Clostridium" to fully
photosynthetic bacteria. Taking known mutation rates and the estimated numbers
of mutations required for the five new proteins, Scherer calculated the
probability that the necessary basic functional states could have evolved.
Assuming a mutation rate of 10-4, "the range of probabilities estimated," he
concluded, "is between 10-40 and 10-104 ... In other words, in 109 years an
FeS-protein may sometimes appear, whereas photopigments and quinones" -- other
proteins required for the evolutionary transition --"are never expected."22
It's a difficult problem for evolutionary theory, to say the least. How, within
the available time, and by known mechanisms, did the necessary bacterial
proteins arise? "From the data presented," concluded Scherer, "the evolution of
cyclic photosynthetic electron transport is an unsolved problem in theoretical
biology. On the basis of present understanding, no solution can be expected."23
That's how the problem looks if we presuppose naturalistic evolution. The tiles
won't go into place. From the perspective of design, however, this research
problem would very likely never arise. Complex systems with interdependent
components, exhibiting specification and small probability, are -- according to
the theory of design -- the products of an intelligent cause. Expressing the
same point proscriptively, we might say that the laws of physics and chemistry
are causally insufficient to generate the specified complexity of organisms, and
that appeals to chance mechanisms are precluded by the Law of Small Probability
(premise 6 of Dembski's argument, given above). The design theorist would take
something like this to be a general law. Starting from that law, the design
theorist would predict that the naturalistic formation of complex biological
systems is probabilistically beyond the realm of the possible.
Such a prediction is, of course, vulnerable to refutation. Indeed, assuming that
exact bounds can be put on theoretical notions such as "specified complexity,"
and that probability estimates can be made rigorously, it should be possible to
run experiments set up precisely to test design-based predictions. In so doing,
the design theorist may be surprised to discover that "unassisted" nature is
capable of more innovation than he suspected. On the other hand, his predictions
may hold true: the specified complexity of organisms may be causally
irreducible.
In short, the design theorist could stumble, or succeed, in any number of ways.
But this is true for all scientists. We always know less than we need to know,
and our theories are never what they should be. These difficulties, of course,
are entirely in keeping with the nature of empirical inquiry. Philosophers of
science have a name for this epistemological difficulty, one of the first they
learn about in their training: the problem of induction.
The problem of induction follows from the necessary finitude of our experience.
All of our claims about the world may be overturned as the compass of our
experience increases. There are only white swans, we say, until a black swan
crosses the lawn. But a black swan might cross the lawn (so to speak) of any
general empirical claim. Design theorists face no special difficulties in this
regard. It might turn out to be the case that any given design-based prediction
does not obtain, but this is possible for any nontrivial prediction entailed by
any theory.
Once we see that "gaps" are theory-dependent, and that design does not propose
to fill the gaps left unsolved by naturalistic evolution, but rather to project
its own pattern of explanation and research problems, all that remains of the
formidable God-of-the-gaps objection is the problem of induction.
And if the "God-of-the-gaps" objection indeed falls under the heading of the
problem of induction, it poses no special challenge to a theory of design. The
finitude of experience is a difficulty common to scientific inquiry and in fact
to human knowledge generally. We could always be wrong! Let philosophical
worries of that sort frighten you, however (any further than they should, which
isn't much), and David Hume will keep you from climbing out of bed in the
morning. The floor might not be there as you step down into your slippers.
Conclusion
Looking over the unfinished mosaic of naturalistic evolution, the design
theorist wants to exclaim, "Let me show you why those problems continue to go
unsolved: the picture guiding your work is false." But he finds his advice is
unwanted, and his understanding of science is rejected as "inserting religion
where it doesn't belong."
In response the design theorist can point to the philosophical shoddiness and
opportunism of narrowly naturalistic construals of scientific explanation. The
game has been rigged against design. But another response appeals to the
skeptical bystander who wonders whether design might not have some real
explanatory power. This bystander doesn't care if the theory requires an
intelligent cause. Such causes are known to exist (human intelligence) or
hypothesized to exist (extraterrestrial intelligence, divine intelligence). This
bystander -- student, scientist, philosopher -- wants to see if design might not
be true.
And that's an interesting question, well worth asking and trying to answer. The
task is to find a good theory of design and to test it.
Notes
[1] W.H. Auden, "The Poet and the City," in the collection The Dyer's Hand.
return to text
[2] In this essay by "theory of design" I mean a theory that seeks to explain
the origin of biological structures. Theories of cosmological or physical design
have of course been formulated; I do not treat them here. return to text
[3] I have elaborated this example (with Dembski's approval) beyond that
actually presented at the symposium, to illustrate the explanatory roles of
Dembski's key notions. return to text
[4] Bertrand Russell, A History of Western Philosophy, New York: Simon and
Schuster, 1945, p. 589. return to text
[5] Charles Darwin, On the Origin of Species, 1st ed., Cambridge, Mass.: Harvard
University Press, 1964; p. 187. return to text
[6] Additional evidence supporting this view has been obtained from "genetic
dissection" experiments. "The favorite object of such studies is the unicellular
Chlamydomonas reinhardii, which was two flagella that propel it through the
water. Many nonmotile mutants have been isolated: in some, the mechanism of
flagellar assembly is defective and the flagella are absent or rudimentary; in
others, flagella are present but immobile. In the latter case, the defect is
likely to be in a protein component of the motor mechanism. Various structural
abnormalities are apparent in electron micrographs of such mutant flagella. ...
In one class of mutants the only detectable change is the loss of the dynein
arms. In a second class the mutants lack only the radial spokes, while in a
third they lack both the central pair of microtubules and the inner sheath. In
all three classes the isolated membrane-free axonemes fail to move in the
presence of ATP" (Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith
Roberts, James D. Watson, Molecular Biology of the Cell, New York: Garland
Publishing, 1983; pp. 567-568). return to text
[7] Darwin, Origin, p. 189. return to text
[8] Timothy Lenoir, The Strategy of Life, Chicago: University of Chicago Press,
1989; p. ix.return to text
[9] Francis Crick, Life Itself, New York: Simon & Schuster, 1981, p. 88.return
to text
[10] Klaus Dose, "The Origin of Life: More Questions Than Answers,"
Interdisciplinary Science Reviews 13 (1988): 348-56; p. 348. return to text
[11] Martin Kreitman, "Will Molecular Biology Solve Evolution?" in Molds,
Molecules, and Evolution, ed. Peter R. Grant and Henry S. Horn, Princeton:
Princeton University Press, 1992; p. 134. return to text
[12] Wallace Arthur, Theories of Life, New York: Penguin Books, 1987; p. 180.
return to text
[13] Bernard John and George Miklos, The Eukaryote Genome in Development and
Evolution, London: Allen & Unwin, 1988; p. 335. return to text
[14] Elliott Sober, "Creationism," chapter Two of Philosophy of Biology,
Boulder: Westview Press, 1993; p. 54. return to text
[15] Ibid., p. 55. return to text
[16] Ibid. return to text
[17] Steven Stanley, The New Evolutionary Timetable, New York: Basic Books,
1981, p. 174. return to text
[18] Sober, "Creationism," p. 55. return to text
[19] Ibid. return to text
[20] Hence, Sober's phrase "the incompleteness of science" is really too
general. The "incompleteness" of which he speaks is always theory-relative, and
thus should be considered in the light of whatever theory is at issue. At any
time, "science" (our body of knowledge about the natural world) will be
incomplete -- necessarily incomplete, one might say. However, from one period to
the next the areas thought incomplete will differ greatly. The "research
problems" of the mesmerist or phlogiston chemist simply do not arise for the
modern psychologist or physical chemist. return to text
[21] Thomas S. Kuhn, The Structure of Scientific Revolutions, Chicago:
University of Chicago Press, 1970; p. 80. return to text
[22] Siegfried Scherer, "Basic Functional States in the Evolution of
Light-driven Cyclic Electron Transport," Journal of Theoretical Biology 104
(1983): 289-299; p. 296. return to text
[23] Ibid., p. 298. return to text
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Promoting an
Understanding of the Intelligent Design of the Universe
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